Contact lenses must be cleaned since soils such as proteins and lipids derived from lachrymal tears may adhere to the lenses. In order to prevent contamination by microorganisms such as bacteria and, it is necessary to disinfect contact lenses which have been removed from the eyes and to preserve them in an appropriate solution until they are worn again. Such treatments for cleaning, disinfection and preservation are unavoidable in safely wearing contact lenses.
However, procedures for cleaning, disinfecting and preserving contact lenses are very complicated. Moreover, several kinds of liquid preparations such as cleaning solution, disinfecting solution and preserving solution must be utilized for these treatments. The trouble and cost required for use and maintenance of contact lenses thus imposes a large burden on the users.
Multi-purpose single liquid preparations for use in conjunction with contact lenses that function for cleaning, rinsing, disinfecting and preservation necessary for the maintenance of the lenses are presently on the market here and abroad. That is to say, these liquid preparations comprise a preserving solution to which surfactant, antibacterial agent and the like are added so that all of cleaning treatment, rinsing treatment, disinfecting treatment and preservation function can be made by the single liquid preparation.
With respect to this type of the liquid preparations for contact lenses, various compounds have been heretofore investigated as antibacterial agents to be added thereto. However, these compounds all must be used in a high concentration for obtaining a practical high antibacterial activity. The use at such a high concentration may raise a problem in safety, since their toxicity is high and there is the danger of irritation to mucous membranes of the eyes and causing inflammation. Thus, investigation has been made so that a higher antibacterial effect can be obtained by the use of a smaller amount of antibacterial agent.
For example, in JP-A-6-321715, it is proposed to use a biguanide derivative in combination with a borate buffer to provide a disinfecting and preserving solution which has a low toxicity to the eyes while having a high level of antibacterial activity. In JP-A-6-504044, it is also proposed to use a biguanide derivative in combination with a tris buffer to provide a disinfecting composition for contact lenses which has substantially no irritation while having an excellent disinfecting property. However, the antibacterial effect of these liquid preparations for contact lenses is still insufficient.
Accordingly, it is an object of the present invention to provide a liquid preparation for contact lenses which can exhibit an excellent antibacterial effect or antiseptic effect while securing a high safety to the eyes.
A further object of the present invention is to provide a liquid preparation for contact lenses which enables a wearer to disinfect the contact lenses directly on the eyes without rinsing them with another rinsing solution.